Work utility stop signal circuit

ABSTRACT

A gated stop signal circuit for detecting when a decelerating cyclically operating device, which takes an indeterminate number of cycles to actually stop, has stopped or is in its last cycle before stopping, and for generating an electrical signal indicating the detected condition. An integrating circuit measures the length of time that the cyclically operating device remains in a particular part of the cycle and triggers the indicating signal when the measured time interval exceeds a predetermined interval known to correspond to the stop condition of the device provided that a second condition exists. Means are provided to selectively cause the occurrence of the second condition. The circuit is illustrated in combination with a needle positioner controlled sewing machine having at least needle down and needle up selectable positions. The circuitry is arranged so that the indicating signal cannot be generated unless the sewing machine is about to stop with the needle in the desired position.

United States Patent [191 Wenrich et a1. t

1 WORK UTILITY STOP SIGNAL CIRCUIT [75] Inventors: Carl M. Wenrich, Shillington, Pa.;

Kalambur G. Ramachandran, Weehawken, NJ

[73] Assignee: Teledyne Mid-America Corporation, Los Angeles, Calif.

[22] Filed: Nov. 21, 1973 [2]] Appl. No.1 417,876

[52] US. Cl. 307/231; 307/234; 307/315; 307/293; 112/219 A; 318/467; 112/219 R [51] Int. Cl. H03k 17/00 [58] Field of Search..... 318/467; 112/219 A, 219 R; 328/111, 129; 307/234, 315, 231, 293

[56] References Cited UNITED STATES PATENTS 3,573,581 4/1971 Datko 112/219 A $582,739 6/1971 Daab 318/467 Primary Examiner-Michael J. Lynch Assistant ExuminerB. P. Davis Attorney, Agent, or Firm-Edelson and Udell Sept. 9, 1975 5 7 ABSTRACT A gated stop signal circuit for detecting when a decelerating cyclically operating device, which takes an indeterminate number of cycles to actually stop, has stopped or is in its last cycle before stopping, and for generating an electrical signal indicating the detected condition. An integrating circuit measures the length of time that the cyclically operating device remains in a particular part of the cycle and triggers the indicating signal when the measured time interval exceeds a predetermined interval known to correspond to the stop condition of the device provided that a second condition exists. Means are provided to selectively cause the occurrence of the second condition. The circuit is illustrated in combination with a needle positioner controlled sewing machine having at least needle down and needle up selectable positions. The circuitry is arranged so that the indicating signal cannot be generated unless the sewing machine is about to stop with the needle in the desired position.

12 Claims, 8 Drawing Figures PATENTED SE? 1975 sum 1 n5 3 FIG. 3

FIG. 3A

SJNCH/POMZE/P INPUT VOLTAGE arwxv TERMINALS 24 AND 2.; I 28 VOLMGE BETWEEN TERMINAL 5 25 25 AND 28 AND a ACROSS RELAY 52 J J A?! 76.38 fitzflu F -w *T; I to VOLTAGE A7 I CAT/1'00! OF I DIODE DIS I'ICvIJC I I you/1a: Ac/Pass CAP/l 6/70)? cf gym a ta OUTPUT 2.9 \F 01'' STOP SIG/VAL Cl/PCU/I' 22 WORK UTILITY STOP SIGNAL CIRCUIT This invention relates generally to a stop signal device utilizable with automatic positioning mechanisms for intermittently operated work utilities. in general, the positioning mechanism functions at the termination of the normal intermittent operation of the work utility to cause certain movable parts of the work utility to come to rest in particular desired positions.

The invention is applicable to a widevariety of devices in a number of different fields, as for example in the garment industry in which power sewing machines are widely used. Generally in such application, it is required that the sewing machine be intermittently operated with periods of non-operation affording an opportunity to shift the position of the item being stitched. in such case, it is most desirable that the needle be in its down position so that the work may be readily turned about it. Some times of course it is more desirable that .the needle be in the up position so that the work may be readily removed from the sewing machine.

Moreover, other types of auxiliary control are also of interest, with such control sometimes being desired at the end of every operating cycle of the work utility, and in other cases such auxiliary control being only desired upon specific operator initiated action. For example, again related to the sewing trades, it may be desired to cause thread severing to occur at the end of some cycles of operation, but not in all cases. Additionally, it may be necessary to have the specific conditions of the work utility known before the auxiliary control system is activated. Such an auxiliary control system is also of course applicable to other devices such as a variety of machine tool operations.

in many auxiliary operations of a sewing machine, such as thread wiping, thread trimming, bed drop and so forth, it is required that such operations not be initiated until the needle has stopped or until it is known that the needle is going through its last cycle before stopping. As will be understood from the description which follows in which the stop signal device is described in conjunction with a sewing machine positioning mechanism, immediately upon actuation of the auxiliary operation control by the operator, the positioning mechanism starts to position the sewing needle, say to its up position. However, in general, it takcs an indeterminate number of machine revolutions before the machine is finally stopped. It is the function of the stop signal circuit to give an electrical signal output when the machine has stopped or when the machine is going through its last cycle before stopping with the needle in the desired position. The output signal is then utilized to actuate the auxiliary operation such as thread trimming or bed drop.

If the auxiliary operation were thread trimming, and the needle were not in its up position, there would be a substantial certainty of needle breakage and jamming of the machine. In the absence of a device such as that according to the invention it would be necessary for the operator to wait until positioning had been completed before actuating the trimming mechanism, a relatively time consuming procedure due to human reaction time. By utilizing the device according to the invention the operator merely actuates the trimming function simultaneously with cessation of sewing, as for example by heeling the power treadle, and trimming occurs automatically at the earliest possible time which cannot (all cause machine damage. Similar consideration of course apply to other auxiliary operations.

A principal object of the invention is to provide a novel stop signal apparatus which generates an output control signal when a work utility which it monitors has stopped or is going through its last cycle before stopping.

Another object of the invention is to provide a novel work utility stop signal device which is inoperative during normal operation of the utility, but which, functioning in conjunction with a work utility positioning mechanism is automatically operative thereafter when the working parts of the utility have been moved to a particular predetermined position to initiate an auxiliary operation.

The foregoing and the objects of the invention will become clear from a reading of the following specification in conjunction with an examination of the appended drawings, wherein:

FIG. 1 is a generalized schematic diagram of the apparatus according to the invention;

FIG. 2 is a schematic diagram of the apparatus according to the invention showing specific application to a positioning mechanism utilized in conjunction with a specifically illustrated stop signal auxiliary control package; and

FIGS. 3A through 3B are a series of time related waveforms illustrating the electrical conditions at dif' ferent points in the circuit during the course of the po sitioning cycle.

In the several figures, like elements are denoted by like reference characters.

Turning now to the drawings, and considering first FIG. 1, there is seen a direct current positioning motor which is to be appropriately coupled to the device to be positioned through any suitable mechanism (not shown), the positioning motor having a field winding MF and an armature MA connected to a source of alternating current 9 by electrical conductors l0 and ll and through intervening control circuit elements. Also coupled to the work utility by means not shown is a synchronizer device designated generally as 12, the synchronizer being provided with a plurality of rotatable rings 13 through 16 which are respectively electrically engaged by adjustable fixed position brushes 17 through 20.

The innermost synchronizer ring 13 is continuously conductive throughout its 360 extent, while the remaining synchronizer rings 14, 15 and 16 each have a conductive section shown in dark line and a nonconductive or barrier section shown in light line. Synchronizer rings 14 and 15 are conductive through most of their extent and have relatively short-arc nonconductive segments which latter are positioned substantially diametrically opposite to one another and correspond therefore to diametrically opposite positions of a rotatable element of the work utility to which the synchronizer rings are affixed as a unit. Synchronizer ring 16 differs from rings 14 and 15 in that its electrically conductive arcuate segment is of relatively short length compared to the remainder of ring 16 which is nonconductive. The conductive portions of all of the synchronizer rings 13 through 16 are electrically interconnected by means of a shorting link 21.

The positioning mechanism is so connected to the work utility that movement of the portion of the work utility which is connected to the movable part of the positioning motor, usually the armature MA, produces a related kind of movement at the movable part of the work utility to which the rotatable synchronizer rings are connected. For example, increasing or decreasing positioning motor speed causes corresponding increasing or decreasing speed of movement of the synchronizer rings 13 through 16, irrespective of whether or not the positioning motor speed and synchronizer ring speed are in fact synchronous.

However, the synchronizer rings are necessarily connected to a movable part of the work utility such that the positions of the rings always exactly correspond to specific positions of the part or parts of the work utility which it is desired to positionally control. For example. when the work utility is a sewing machine, the non conducting segments of synchronizer rings 14 and 15 could correspond to particular positions of the sewing machine needle, as for example an up position and a down position, and in such case, the conductive segment of outer synchronizer ring 16 would always correspond to a third position of the needle which is neither up nor down but at a specific position therebetween. Such a position could for example be the position where the needle has gone through its down position and is on its travel upward to the up position.

In a sewing machine mechanism, the synchronizer rings could conveniently be connected to the spindle shaft since the latter performs one complete revolution for each complete reciprocating cycle of the sewing machine needle bar to provide an invariant synchronized relationship between movement of the sewing machine needle and the positions of specific parts of the synchronizer rings such as the non-conducting segments of rings 14 and 15 and the conducting segment of ring 16. Automatic positioning is carried out by controlling the running and braking of the DC positioning motor through the synchronizer ring structure in the manner described in detail in the co-pending U.S. patent application of Carl M. Wenrich and Bryce E. Hoverter, .lr. entitled Automatic Positioning Mechanism" and assigned to the assignee of this application. The positioning mechanism itself is not a part of the present invention, and any other device suitable for effecting positioning could be used as well.

Additional controlled functions can also be carried out by means of an auxiliary control package designated generally as 22. The auxiliary control package 22 is provided with six terminals 23 through 28 by means of which the synchronizer l2 and other elements of the circuit to be described determine when the auxiliary control package 22 produces a pre-determined condition at terminals 29 of the control package to thereby actuate an auxiliary device such as a thread trimmer.

Auxiliary control package terminal 23 connects to synchronizer brush through a control line 30. Terminal 24 connects via a control line 31 to the contact of a switch 81 shown in an open circuit condition, the pole of the switch S1 being connected to the cathodes of a pair of rectifier diodes D1 and D2 connected in a fullwave rectification circuit to the opposite ends of secondary windin g 33 of power transformer 34, the primary winding of which is connected to power source 9. Auxiliary control package terminals 26 and 27 are connected respectively to a pair of control lines 35 and 36 which themselves connect respectively to one end of the coil 37 of a relay 38 and to the contact of a normally open switch $2, the control lines 35 and 36 being shown as short-circuited by a removable shorting link 39. The opposite end of relay coil 37 is connected through a removable shorting link 40 to the control line 31 and the contact of switch S1, while the pole of switch S2 is returned via conductor 41 to the center tap of transformer winding 33. Auxiliary control package terminal 28 is connected to the center tap of transformer winding 33 by means of control line 42 which connects to conductor 41.

Control line 31 also connects via conductor 43 to one pole 44 of relay 38, the pole 44 being normally engaged with contact 45 which is connected to synchronizer brush 19 when the coil 37 of relay 38 is de-energized. A second pole 46 of relay 38 is connected to the lower end of relay 37 and is open-circuited when the relay coil 37 is de-energized. When relay coil 37 becomes energized, the pole 46 transfers to contact 47 and completes a holding current circuit via conductor 48 to the center tap of transformer winding 33. At such time, of course, relay pole 44 transfers from contact 45 to contact 49 and thereby connects synchronizer brush 18 to control line 31 while simultaneously disconnecting synchronizer brush l9 therefrom.

As will be subsequently understood, switch S1 is the master control switch which when open-circuited as shown disables the entire positioning mechanism and auxiliary control package. Switch S1 in operation is normally open while the work utility is being operated, and is automatically closed when operation of the work utility is terminated by the operator. For example, switch S1 could be connected to the treadle of a sewing machine so that when the operator releases the treadle to terminate stitching, switch 81 would automatically close to thereby initiate a positioning cycle. The function of the switch S2 is to energize relay 38 either through the auxiliary control package 22 or directly through switch S2 as desired in order to transfer control of conditions on control line 32 from synchronizer brush 19 to synchronizer brush 18 should that be desired.

Considering first the actuation of an auxiliary control cycle by means of a synchronizer l2 and auxiliary control package 22, when switch S1 closes at the termination of the work utility operating cycle, electrical current flows from the fullwave rectified supply previously described, through closed switch S1, over control line 31 to terminal 24 of the auxiliary control package 22 and also downward through conductor 43 to pole 44 of relay 38 and through relay contact 45 to synchronizer brush 19. Since the work utility is still running but is coasting downward in speed, the synchronizer rings are rotating, and during the time interval when brush 19 is on the conductive portion of synchronizer ring 15 current flows therethrough to the synchronizer shorting link 21 and consequently to the conductive portions of the other synchronizer rings 13, 14 and 16. Current thus flows through synchronizer ring 13 to brush l7 and outward to control line 32 and contact 25 of the auxiliary control package 22.

Current may also be lead from control line 32 downward through conductor 50 to the coil 51 of relay 52 and back to the power supply via conductor 41. Current simultaneously flows through diode D6, resistor R1 and through the parallel arrangement of capacitor C1 and coil 53 of relay 54, energization of relay coil 53 being delayed for a period of time determined by the charging time constant of the resistive capacitive network formed by R1 and Cl. Relays 52 and 54 in conjunction with the synchronizer 12 control the positioning motor and will not be considered in more detail hereinafter.

When switch S1 closed, terminals 24 and 28 of the auxiliary control package 22 were connected respectively by conductors 31 and 42 to the positive and negative terminals of the DC power supply and provide a source of continuous DC power for energizing the circuitry and mechanisms within the control package which require such power. Control line 32 which leads to terminal 25 of the auxiliary control package from brush 17 of the synchronizer has positive voltage on it as long as synchronizer brush 19 is in contact with the conductive portion of synchronizer ring 15, the voltage at terminal 25 being interrupted for the time interval during which the synchronizer brush 19 is in engagement with the non-conductive segment of ring 15. Consequently, a timed pulse condition is presented to terminal 25 once for each revolution of the synchronizer rings and the timing of the pulse is synchronized with the particular position of the work utility such as the needle of the sewing machine. In the illustrated and previously described case, this corresponds to a timed indicator of the down position of the sewing machine needle.

Terminal 25 of the auxiliary control package 22 can also be provided with a timed pulse signal indicative of the up position of the sewing machine by switching the supply power present on control line 31 from synchronizer brush l9 and ring to synchronizer brush l8 and ring 14. This is accomplished merely by momentarily closing switch S2 which energizes relay coil 37 of relay 38 from the power supply through switch S1 and shorting links 39 and 40. This causes the poles 44 and 46 of relay 38 to transfer respectively to contacts 49 and 47. Switch S2 need not be held closed to maintain relay 38 energized because of the holding current circuit provided by relay contact 47 and pole 46.

Control line 30 which connects synchronizer brush 20 with terminal 23 of the auxiliary control package 22 is a second timed event controlled signal line in which the timed signal pulse appears at terminal 23 when the synchronizer ring 16 rotates to the position where its conductive segment contacts the brush 20. For illustrative purposes this is illustrated as occuring at a time different from the timed indications of the down position and up position of the needle bar and can represent any point whatever in the interval which is desired by the particular application of interest. For example, if it is desired to initiate an event at a predetermined point in the cycle corresponding to a particular physical positioning of the work utility with respect to a specific state of the work utility, such as a point in the cycle between the needle down and needle up positions of a sewing machine, then it is necessary to not only know when the needle down reference condition occurs but it is also necessary to have an indication thereafter of the occurrence of the desired condition. Such an indicator is of course provided by synchronizer ring 16 and the signal which it generates on control line 30.

In the event that it is desired that the signal pulse indicating the occurrence of the timed event which appears on control line 30 should not be operative to produce a particular result until a pre-selected other condition shall have occurred, such a result can be obtained for example by removing the shorting link 39 so that the switch S2 wher closed does not actuate relay 38 independently of the auxiliary control package 22. By way of illustration in the case of a sewing machine operation, it may be desired that the implementation of the controlled event controlled by the signal state at terminals 29 of auxiliary control package 22 shall not occur unless the sewing machine needle is in its up position. Consequently, it is necessary that relay 38 be actuated to cause the timed event control signal on line 32 to be determined by up position ring 14.

With shorting link 39 removed from the circuit, closure of the switch S2 requires that energization of relay coil 37 be accomplished by a current flow through control lines and 36 connected to terminals 26 and 27 of the auxiliary control package. The internal circuity of the auxiliary control package may then be arranged so that no controlled event at terminals 29 can be initiated prior to the establishment of the current flow through the control package 22 via control lines 35 and 36 irrespective of the occurrence of the timed event control signals which cyclically appear on control line 30. Such controlled condition, in which up positioning and auxiliary operation cannot occur until the down position stop condition has been established, is illustrated in the circuit of FIG. 2 to which attention should be now directed.

It is observed that FIG. 2 is the same as FIG. 1 excepting that shorting link 39 has been removed, diode D12 has been connected across coil 37 of relay 38, and shorting link 40 has been replaced with a normally closed switch section 53B ganged with switch section 83A which together form inching switch S3 in place of the single section switch S3 of FIG. 1. The removal of shorting link 39 is required to transfer timing control of up positioning to the stop signal circuit 22 when switch S2 has been closed. The function of diode D12 is to suppress the voltage spike generated by relay coil 37 when deenergizing to protect Zener diode Z in the stop signal circuit 22. Operation of the inching switch S3 is referred to hereinafter.

As shown in FIG. 2, when the switch S1 closes at the termination of the work utility operating cycle, current flows from the power supply through line 31 to line 43 and stop signal circuit terminal 24, from line 43 to relay pole 44 and contact 45 to synchronizer brush 19, through synchronizer ring 15 and shorting link 21 to synchronizer ring 13, through brush l7 and line 32 to stop signal circuit terminal 25 and also to conductor which latter energizes relay coils 51 and 53 of relays 52 and 54 respectively. Energization of relays 52 and 54 starts the positioning mechanism into operation which consists of a series of forward rotations of the spindle shaft alternated with periods of strong braking action.

The running and braking of the positioning motor is controlled by turn-on and turn-off of the silicon controlled rectifiers SCRl and SCRZ by the direct current and phase-shifted alternating current provided by transformer winding 57 through the poles and contacts of relays 52 and 54.

The rotational speed of the work utility, and hence of the synchronizer rings, is being quickly reduced by the associated braking and positioning devices so that the time periods of both conduction and non-conduction through the synchronizer rings are increasing with each rotation of the synchronizer. This condition is shown in the waveforms of PK). 3 to which attention should be directed. FIG. 3A shows the synchronizer input voltage and the voltage between stop signal circuit terminals 24 and 28 as determined by the condition of switch S1. When the switch is open during operation of the work utility the voltage is at zero level, and when switch S1 closes at the end of operation of the work utility the voltage rises to the plus level illustrated and remains there continuously until such later time as switch S1 is again opened by reactivation of the work utility, as illustrated at the right hand end of FIG. 3A. During this time capacitor C7 charges through potentiometer P2 toward the zener clamp voltage of zener diode 2.

FIG. 38 illustrates the voltage between stop signal circuit terminals 25 and 28 and across the coil 51 of relay 52 and corresponds to the voltage appearing at brush 17 of the synchronizer which is in contact with the completely conductive synchronizer ring 13. Since it was assumed as an initial condition that the synchronizer brush 19 was engaged with a conductive portion of synchronizer ring when switch S1 closed, the voltage appearing at terminal 25 immediately rises to the plus level and remains there for the interval ll shown, until the barrier portion of the synchronizer ring is reached. When the barrier is reached the voltage is interrupted and drops to zero level, remaining there for the time interval 12 during transit of the barrier por' tion past the brush l9, and then rises again to the positive level. As the synchronizer slows down due to the action of the positioning motor, the time length of each of the succeeding cycles of synchronizer conduction I3, 15, t7, :9, and non-conduction r4, t6, t8 and tD increases in length as is shown in FIG. 313 until the work utility comes to a complete stop with the synchronizer brush 19 resting on the non-conducting barrier strip of ring 15 so that the voltage at terminal 25 drops to and remains at the zero level as shown. Thus, the electrical signal at terminal 25 from the synchronizer is a series of successively lengthening pulses until the machine stops.

It is possible to detect the speed and deceleration of the machine during any cycle from these pulses, and the time that the needle spends in the down position for a given system can also be detected. It has been found statistically that the needle spends less than a particular time interval in the down position if the machine is not at the verge of stopping. In other words, if the needle spends more than a particular time interval, say ID, in the down position then the machine is either in its last cycle or is about to stop. Of course, while the time intervals vary with the machine speed, the circuit detects when the machine spends more than a selected time interval tD in the down position, and immediately gives an electrical signal called hereinafter the critical voltage V, and it is possible to set the circuit to detect different selected values of [D for different system set-ups.

Each pulse at terminal 25 is reduced in amplitude to a few volts, filtered by the network of R7, C6, R8, R9 and applied to the base emitter electrodes of transistor T1. These positivegoing pulses turn on transistor T1 which thereby completely discharges capacitor C7. When the pulses drop to the zero level during times I2, [4, 16, t8 and ID, transistor T1 is cut-off and capacitor C7 charges to the voltages as shown in FIG. 3D. The charging time of C7 is thus controlled by the length of time that T1 remains cut-off, so that as T1 remains cutoff for successively longer times C7 charges to successively higher voltage levels. The rate of charge of C7 is determined by the time constant P2C7 which is con trollable by movement of the arm of potentiometer P2, and consequently, the length of time required for C7 to charge to the critical voltage V is settable by P2 to be just slightly longer than the time interval tD so that when the critical voltage V is reached it is known that the work utility is about to stop or has just stopped.

The critical voltage V is that voltage sufficient to overcome the cut-off bias provided to the Darlington circuit T2T3 by series diodes D13 and D14 and thereby turn on T2T3 resulting in sharp pull-down of the potential at the junction of T2 and T3 collector electrodes and the cathode of diode D15 as shown at the right hand end of FIG. 3C. Turn-on can only occur when the cathode end of D14 is connected to the DC power supply return line 41 by the closure of switch S2. The turnon current T2T3 is supplied by C7, and as shown in FIG. 3D the voltage on capacitor C7 is held at the critical voltage V with the bias current being supplied from the zener controlled positive terminal of the DC power source.

With D15 clamped low by T2T3, the terminal 29 connected to the anode of D15 is also clamped low. Consequently, when the other terminal 29 which is connected to terminal 23 goes high in potential because of contact between brush 20 and the conductive segment of synchronizer ring 16, a pulse 64 appears at terminals 29 as shown in FIG. 3E. It is this pulse 64 which is the stop signal circuit output pulse utilized to actuate the auxiliary operation device such as a thread trimmer or bed drop mechanism.

Synchronizer ring 16 and brush 20 may be so oriented with respect to ring 14 and brush 18 that brush 20 passes out of contact with the conductive segment of ring 14 before a complete stop occurs in which case pulse 64 will be of finite duration and will terminate. On the other hand, if brush 18 does not pass out of contact with the conductive segment of ring 14 before a complete stop occurs then pulse 64 will constitute a step function that terminates when the synchronizer input voltage, as shown in FIG. 3A, returns to zero level upon the opening of switch S1.

The generation of output pulse 64 just described was predicated upon closure of switch S2 to connect the cathode of bias diode D14 to the negative side of the direct current supply. Closure of switch S2 is necessary to cause up positioning of the sewing machine needle, and it is apparent as previously discussed, that thread trimming for example cannot be carried out with the needle in its down position. Accordingly, unless up positioning of the needle is effected, no pulse 64 can be generated at terminals 29. This lockout system func tions as follows.

As shown, pole 44 of relay 38 normally connects the direct current supply through switch S1 to the down position synchronizer brush l9 and ring 15 so that normally the machine will stop with the needle in the down position under control of the positioning mechanism. Additionally, stop signal circuit 22 produces a critical voltage V across capacitor C7 when the machine is just about to stop in the down position, and this voltage V attempts to turn on the Darlington circuit of T2T3. It cannot however do so because the voltage across C7 is much lower than the effective bias between the base of T2 and emitter of T3. This results from the fact that closure of switch S1 also causes a very small current to flow through switch S38, coil 37 of relay 38, conductor 35, resistors R12 and R11 back to the negative return 11?. perhaps in. the nrtlw it larger Rusistm" l E2 is r-l' sulI it'imit uhsululu ldHkE tn prevent, pullin of min 33. {,i'lilhtlqtltilllj [lie T213 Cllillll. is hiri'ustl strunglp into mm-wunductiun 1w Stllh illlliliy the; lilll (limp? :mil (1'? s mmipat'l ml ilvvrrlirp lig sulli iimit voltage tintlcr may I t liic utilhwlt: iul' ii at the plus (l) clil tiliics imv liuiiglr.

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4. A device as described in claim 1 wherein said biased swith comprises a first transistor circuit biased to cut-off by a fixed bias circuit, and said event timer comprises a series resistor-capacitor charging circuit in which the capacitor is connected across the input circuit of said first transistor circuit and is also connected directly across the output circuit of a second transistor circuit which forms part of said event timer, the input circuit of said second transistor circuit being coupled to said sensing means to receive said first sensing signals therefrom, whereby, said second transistor circuit conducts strongly in the absence of said first sensing signals to prevent charging of said capacitor and maintain said first transistor circuit in its cut-off state, and said second transistor circuit is cut-off in the presence of said first sensing signals to permit charging of said capacitor toward a critical voltage level sufficient to overcome the fixed bias of said first transistor circuit and turn on the latter, said critical voltage level being reached when said work utility movable part has slowed sufficiently for one cycle of said first sensing signal to persist for a time duration greater than the aforesaid predetermined minimum time.

S. A device as described in claim 1 further including stop signal device disabling means operatively coupled to the work utility and effective to disable said stop signal device whenever the work utility is being operated.

6. A device is described in claim 1 wherein said biased switch comprises a gate circuit having an input and an output and being normally closed by a bias circuit, and said event timer comprises an integrating circuit including an integrating element which is connected to the gate circuit input and is shunted by the output circuit of an electronic switch whose input circuit is coupled to said sensing means to receive said first sensing signals therefrom, the output circuit of said electronic switch becoming a shortcircuit across said integrating element in the absence of said first sensing signals at its input circuit and becoming an open circuit across said integrating element in the presence of said first sensing signals at its input circuit, whereby, said electronic switch when an open circuit permits a rise of potential across said integrating element toward a critical signal potential sufficient to overcome the gate closing effect of said bias circuit and open said gate circuit, said critical signal potential being reached when said work utility movable part has slowed sufficiently for one cycle of said sensing signal to persist for a time duration greater than the aforesaid predetermined minimum time.

7. A device as described in claim 4 wherein said resistor-capacitor charging circuit of said event timer is charged from a fixed potential source of regulated direct current and the time constant of said charging circuit is selectively variable to adjust for the characteristics of different work utilities.

8. A device as described in claim 4 wherein both said first and second transistor circuits are characterized by a relatively high impedance input circuit and a low impedance output circuit.

Q. A device as described in claim 4 further including an auxiliary bias circuit connected into the input circuit of said first transistor circuit operative to increase the bias on said first transistor circuit sufiiciently far into its cut-off region to prevent turn on of said first transistor circuit irrespective of the voltage level across the capacitor of said charging circuit, and selectively actuatable auxiliary bias circuit defeat means effective when actuated to nullify said auxiliary bias circuit and reduce the bias to that of said fixed bias circuit.

10. A device as described in claim 6 further including,

a. an auxiliary bias circuit connected to said gate circuit and operative to increase the gate-closing bias sufficiently to prevent opening of said gate irrespective of the signal potential on said integrating element,

b. selectively actuatable auxiliary bias circuit defeat means efiective when actuated to nullify said auxiliary bias circuit and reduce the gate-closing bias to that of said bias circuit,

. sensing means second means which generates a second sensing signal during a second portion of each cycle of movement at a predtermined fixed fraction of the cycle displaced from the generation of said first sensing signal and indicates a second particular position of the movable part of the work utility,

d. a pair of output terminals one of which is coupled to said sensing means second means and the other of which is coupled to the output of said gate circuit,

whereby, when said gate circuit is open the occurrence of a second sensing signal indicates at said pair of output terminals that the movable part of the work utility is about to stop within one cycle and has already moved to the said second particular position.

11. A device as described in claim 10 wherein said auxiliary bias circuit defeat means includes control means operative through said sensing means to actuate an auxiliary device when said gate circuit is open.

12. A device as described in claim 10 wherein said auxiliary bias circuit defeat means includes gate locking means operative to lock said gate circuit open after said gate circuit has been opened by said event timer. It IF i 

1. A stop signal device for detecting that a cyclically movable part of a work utility is about to stop or is to stop during the next cycle of movement, comprising in combination, a. sensing means coupled to and synchronously movable with the cyclically movable part of the work utility, said sensing means having first means which generates a first sensing signal during a first portion of each cycle of movement of the work utility movable part and indicates a first particular position of the movable part of the work utility, which first sensing signal is indicative of the time duration of the said first portion of the cycle of movement, b. a biased switch having an input circuit and an output circuit, the bias on said switch causing a first condition at said output circuit when said input circuit is in a first state, and said input circuit when in a second state overiding the switch bias and causing a second condition at said output circuit, c. an event timer having an input circuit coupled to said sensing means to receive said first sensing signals and having an output circuit coupled to the said biased switch input circut, said event timer causing said biased switch input circuit to be in its said first state so long as said first sensing signal indicates a time duration less than a predetermined minimum time and causing said biased switch input circuit to be in its said second state when said first sensing signal indicates a time duration greater than the aforesaid predetermined minimum time, whereby, the occurrence of said second condition at said biased switch output circuit signals that the cyclically movable part of the work utility is about to stop or will stop during the next cycle of movement.
 2. A device as described in claim 1 wherein said sensing means further includes second means which generate a second sensing signal during a second portion of each cycle of movement, which second sensing signal is generated at a predetermined fixed fraction of a cycle of movement displaced from the generation of said first sensing signal and indicates a second particular position of the movable part of the work utiLity, said second sensing signal being coupled to one of a pair of output terminals of which the other terminal is coupled to the said output circuit of said biased switch, whereby, the occurrence of said biased switch output circuit second condition at one output terminal and the occurrence of a second sensing signal at the other output terminal indicates that the movable part of the work utility will stop within one cycle and has already moved to the said second particular position.
 3. A device as described in claim 1 further including selectively actuatable bias change means coupled to said biased switch effective when deactuated to increase the bias to a level effective to prevent the occurrence of the said second condition at the output circuit of said biased switch irrespective of the state of said biased switch input circuit, and effective when actuated to decrease the bias to a level responsive to the state of said biased switch input circuit.
 4. A device as described in claim 1 wherein said biased swith comprises a first transistor circuit biased to cut-off by a fixed bias circuit, and said event timer comprises a series resistor-capacitor charging circuit in which the capacitor is connected across the input circuit of said first transistor circuit and is also connected directly across the output circuit of a second transistor circuit which forms part of said event timer, the input circuit of said second transistor circuit being coupled to said sensing means to receive said first sensing signals therefrom, whereby, said second transistor circuit conducts strongly in the absence of said first sensing signals to prevent charging of said capacitor and maintain said first transistor circuit in its cut-off state, and said second transistor circuit is cut-off in the presence of said first sensing signals to permit charging of said capacitor toward a critical voltage level sufficient to overcome the fixed bias of said first transistor circuit and turn on the latter, said critical voltage level being reached when said work utility movable part has slowed sufficiently for one cycle of said first sensing signal to persist for a time duration greater than the aforesaid predetermined minimum time.
 5. A device as described in claim 1 further including stop signal device disabling means operatively coupled to the work utility and effective to disable said stop signal device whenever the work utility is being operated.
 6. A device is described in claim 1 wherein said biased switch comprises a gate circuit having an input and an output and being normally closed by a bias circuit, and said event timer comprises an integrating circuit including an integrating element which is connected to the gate circuit input and is shunted by the output circuit of an electronic switch whose input circuit is coupled to said sensing means to receive said first sensing signals therefrom, the output circuit of said electronic switch becoming a shortcircuit across said integrating element in the absence of said first sensing signals at its input circuit and becoming an open circuit across said integrating element in the presence of said first sensing signals at its input circuit, whereby, said electronic switch when an open circuit permits a rise of potential across said integrating element toward a critical signal potential sufficient to overcome the gate closing effect of said bias circuit and open said gate circuit, said critical signal potential being reached when said work utility movable part has slowed sufficiently for one cycle of said sensing signal to persist for a time duration greater than the aforesaid predetermined minimum time.
 7. A device as described in claim 4 wherein said resistor-capacitor charging circuit of said event timer is charged from a fixed potential source of regulated direct current and the time constant of said charging circuit is selectively variable to adjust for the characteristics of different work utilities.
 8. A device as described in claim 4 wherein botH said first and second transistor circuits are characterized by a relatively high impedance input circuit and a low impedance output circuit.
 9. A device as described in claim 4 further including an auxiliary bias circuit connected into the input circuit of said first transistor circuit operative to increase the bias on said first transistor circuit sufficiently far into its cut-off region to prevent turn-on of said first transistor circuit irrespective of the voltage level across the capacitor of said charging circuit, and selectively actuatable auxiliary bias circuit defeat means effective when actuated to nullify said auxiliary bias circuit and reduce the bias to that of said fixed bias circuit.
 10. A device as described in claim 6 further including, a. an auxiliary bias circuit connected to said gate circuit and operative to increase the gate-closing bias sufficiently to prevent opening of said gate irrespective of the signal potential on said integrating element, b. selectively actuatable auxiliary bias circuit defeat means effective when actuated to nullify said auxiliary bias circuit and reduce the gate-closing bias to that of said bias circuit, c. sensing means second means which generates a second sensing signal during a second portion of each cycle of movement at a predtermined fixed fraction of the cycle displaced from the generation of said first sensing signal and indicates a second particular position of the movable part of the work utility, d. a pair of output terminals one of which is coupled to said sensing means second means and the other of which is coupled to the output of said gate circuit, whereby, when said gate circuit is open the occurrence of a second sensing signal indicates at said pair of output terminals that the movable part of the work utility is about to stop within one cycle and has already moved to the said second particular position.
 11. A device as described in claim 10 wherein said auxiliary bias circuit defeat means includes control means operative through said sensing means to actuate an auxiliary device when said gate circuit is open.
 12. A device as described in claim 10 wherein said auxiliary bias circuit defeat means includes gate locking means operative to lock said gate circuit open after said gate circuit has been opened by said event timer. 